In configuring the display unit for an aircraft navigational computer system such as a system that utilizes very low frequency radio signals in combination with the Omega system, the provision for maximizing the function and display area of the display unit must be balanced against the very limited availability of flight panel areas in the typical aircraft cockpit. Various human factor considerations are also very important with respect to the design of the display and the operation of the system. Such factors include the nature and location of the display as well as the type and location of the operator actuated data input and function means. It is also highly desirable to provide for ease of maintainability of the display unit especially in smaller aircraft such as those used in corporate flying.
In addition, to be fully effective, the controlled display unit must provide a readable display in all conditions including bright sunlight. In order to enhance viewability of the display, reflections should be eliminated from the viewing surface of the display.
Heretofore one approach used to provide a cathode ray tube type display with a high contrast ratio has been to use a phosphor that has a very narrow spectral emission band and then to bond a matching glass filter having a narrow band transmittance that matches the phosphor emission band directly to the face of the cathode ray display screen. Reflections are eliminated by depositing a reflection reducing coating to the viewing surface of the glass filter bonded to the CRT. This approach has proven to be quite costly both in terms of materials and in terms of manufacturing since close tolerances are required to bond the glass filter to the CRT and to apply the reflection reducing coating.